In the Hokuriku district in Japan, large numbers of concrete structures have been suffering from damage caused by alkali silica reaction (ASR). Some huge volcanoes are located within this district, and the headwaters of main rivers prompt the outflow and spreading of volcanic rocks such as andesite, rhyolite and tuff stones, which are the main volcanic reactive stones causing the serious damage of ASR in the entire area. To solve this problem effective countermeasures such as repair and strengthening methods should be established.

One intake tower in this area had deteriorated due to ASR, and deformation had occurred as a consequence of ASR ex-pansion of the concrete. Countermeasures were carefully considered by academic experts, and post-tensioned tendons were inserted into the intake tower concrete (vertically oriented) so that the power station can continue to operate safely in the future. This is thought to be the first challenge of its type anywhere in the world for which the deformation of a real structure caused by ASR expansion must be controlled.

In this paper, the results obtained from laboratory tests using reactive aggregate and the overview of the investigation and the method of the reinforcement including the effect of the countermeasures will be discussed.